This invention relates to an improved circuit arrangement for buffering data between an asynchronous signal source, e.g., a manual alphanumeric keyboard and an output device, e.g., a controller feeding a printer which is arranged to accept information on an asynchronous basis.
In the case of fully mechanical teletypewriters, teleprinters, etc., there is direct physical linkage between the input keys, e.g., alphanumeric and symbol keys on a keyboard and the printing arrangements which react to those keys. Accordingly, the operator is constrained to maintain a rate of key manipulation which is consistent with the ability of the print mechanism to respond and conversely there is little time delay between key actuation and printing response. Where a source of input information, e.g., a manually operated alphanumeric keyboard is not mechanically coupled to the output printing arrangements, buffer data storage is often introduced between the input device and the printing device. Such buffer storage serves to smooth out variations in typing speed and thus permits printing of all the information without loss. A buffer storage arrangement introduces time delay and thus appears to decouple the keyboard and the print mechanism. Such delay is not desirable but generally can be tolerated. There is, however, one circumstance (character repeat) in the operation of teleprinters in which delay incurred by buffer storage creates an operating problem.
It is common to provide a repeat key in the alphanumeric keyboard of a teleprinter; and in normal manipulation of the keyboard, a character key and a repeat are simultaneously depressed to generate a sequence of like characters. When delay is introduced in the transmission of such repeated characters from a keyboard to a printing device, it is difficult for the operator to accurately define the desired end of a sequence of repeated characters.